Application of different turbulence closure model for stratified tidal flows and salinity in an estuarine system

Transient stratification in estuaries reflects competition between the stratifying influences of the vertical gravitational circulation and longitudinal density gradient by vertical shear, set against the mixing influence of, principally, tidally generated turbulence. A vertical (laterally averaged) two-dimensional model of an estuary, using seven different parameterizations of vertical mass and momentum mixing coefficients from the literature, is used to make general predictions about the nature of the time-dependent stratification, velocity field and salinity in an estuary. The downstream boundary, at the river mouth, is an M2 tide with amplitude being half of the mean tidal range to force the model runs for numerical experiments. The results show the Mellor and Yamada scheme products larger stratification, density gradients and have less vertical mixing. Model calibration and verification is performed to use parameterization of mixing coefficients against observational data of salinity. The root-mean-square (RMS) errors and mean absolute errors are used as qualitative and quantitative criteria. The results show Park and Kuo scheme performs best. Mellor and Yamada scheme over-predict the amplitude of the stratification signal. The other schemes, such as Thompson, Lehfeldt and Bloss, Pacanowski and Philander, and Munk and Anderson, over-predict the maximum salinity.